The invention relates generally to roll-forming apparatus, and more particularly to corrugating rollers for producing corrugated sheet material.
Typically, corrugating operations are performed by passing sheet material, commonly referred to as the "medium" in the corrugated paper industry, through the nip point of a pair of large rollers having undulating flutes. Such rollers are typically mounted for rotation in corrugating apparatus commonly referred to as a "single facer". The corrugating surfaces of such rollers are usually hardened for increased wear resistance by various processes known to those skilled in the art. In the hardening process, care must be taken to avoid overly hardening the shaft portion of the roller, thereby making it too brittle.
It is frequently desirable to heat at least one of the rollers by passing steam through an internal chamber in order to facilitate the forming of the medium. Additionally, one of the pair of such rollers may also include axially-spaced circumferential slots for receiving a semi-circular finger partially circumscribing on the opposite roller in order to maintain the formed medium in contact with such opposite roller. Alternatively, so-called "fingerless" single facers employ a vacuum system for retaining the medium in place.
One problem typically encountered in such corrugating apparatus is the noise level generated by the high-frequency impacts of the tips and valleys of the rollers. This noise level, amplified by the further resonance throughout the rollers, may exceed permissible levels, thereby necessitating ear protection for personnel working the area. Another problem is that a foreign object, such as a bolt or nut, passing through the nip point of the rollers may bend, break, or otherwise damage one or more of the flutes, thereby ruining a very expensive set of corrugating rollers. Still another problem related to the manufacture of forming rollers is that any error in manufacturing the roller surface may necessitate the scrapping of the entire roller, which is extremely costly.
According to the present invention, a forming or corrugating roller includes a plurality of forming discs coaxially mounted on an elongated cylindrical mandrel. The axial thickness of each disc is preferably thin relative to its diameter in order to provide a substantial number of abutting faces which tend to reduce the noise by frictional damping. The circumferential surfaces of the discs have undulating flutes that form the corrugating surface. Since the discs are not an integral part of the mandrel, they may be formed and hardened before being mounted on the mandrel. Furthermore, in the event of an error in the manufacture of the functional surface, or an accidental damaging of the flutes, only the affected discs are scrapped instead of the entire roller.
The forming discs, which are secured for rotation with the mandrel, may optionally include irregularly-shaped axially-extending openings located in an irregular pattern to provide a varying resonant frequency, thereby reducing noise caused by the contact of the flutes on the rollers. The mandrel may also include a sound-absorbing material thereon, and sound-absorbing spacers may be inserted between adjacent discs. In order to provide the required rigidity, strength, sound absorption, and reliability of the roller assembly, each disc is secured to its adjacent discs preferably by relatively short axially-extending fasteners. Finally, the discs may also optionally include aligned openings extending axially therethrough for vacuum retention of the material to be formed in a fingerless forming machine configuration, or alternatively, channels or other fluid conduits communicating with an internal vacuum chamber in the mandrel for the same purpose. If vacuum retention is accomplished by such axial openings through the discs, the mandrel may include internal heating means.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.